1. Field of the Invention
This invention relates generally to an optical system. More particularly, it relates to a photolithographic optical reduction system used in semiconductor manufacturing.
1. Related Art
Semiconductors are typically manufactured using various photolithographic techniques, which are implemented using complex optical systems. For example, one complex optical system used in the manufacturing of semiconductors is a photolithographic optical reduction system. While these complex optical systems perform adequately for their intended purposes, these systems have certain limitations that affect the minimum size of component features that can be accurately reproduced on a semiconductor chip. One such limitation is lens position and/or alignment.
As semiconductor manufacturers strive to produce smaller semiconductor features, minor positioning errors or misalignment of lenses in photolithographic optical reduction systems will have an effect on the minimum size of component features that can be accurately reproduced. In addition, minor changes in the optical or mechanical properties of the photolithographic optical reduction systems over time, for example, due to variations in environmental temperature or compaction of the lenses of a system, will also have an effect on the minimum size of component features that can be accurately reproduced. Optical imaging, lens position and alignment can be compromised by all sorts of changes that occur in the mechanical properties of materials over time, due for example to effects such as creep. Furthermore, lens position and/or alignment can also change due to forces and loads experienced during shipping and handling of these photolithographic systems. As would be known to a person skilled in the relevant art(s), each of these listed changes, and others, affect the size of semiconductor features that can be accurately reproduced.
In the past, the lenses in a photolithographic optical system have been positioned and aligned manually using, shims, adjustment screws, and other alignment techniques. In a typical system, lenses are held by lens rings, which are contained within a lens housing. The position of some or all of the lens rings within the lens housing can be determined, for example, by manually adjusting a series of adjustment screws. While this manual system and technique provides adequate alignment; this manual system and technique cannot correct or compensate for environmental factors and/or minor misalignments of lenses, and other changes of the lenses that occur during semiconductor production and over time. A better active alignment system and technique will allow for the production of smaller semiconductor features and correction of changes, including those listed herein, that limit the size of semiconductor features that can be accurately reproduced.
What is needed is an apparatus, system, and method for precision positioning and alignment of a lens in a complex optical system. The apparatus, system, and method should permit extremely small and precise adjustments to be made to the position of the lens while the optical system is in use.
The present invention provides an apparatus, system, and method for precision positioning and alignment of a lens in an optical system. In an embodiment of the present invention, a first support for coupling to the peripheral edge of the lens is mechanically connected to a second concentric support using a plurality of positioning devices. At least one positioning device is configured to move the first support in an axial direction relative to the second support. A second positioning device can be used to move the first support relative to the second support in a direction substantially perpendicular to the axial direction.
Each positioning device comprises a lever, an actuator, and a flexure. The lever has a pivot point and is mounted on the second support. The actuator is connected to the lever and used to operate the lever about its pivot point. The flexure has a first end connected to the lever between the actuator and the pivot point. A second end of the flexure is connected to the first support. In a preferred embodiment of the present invention, the flexure is connected to the lever using a screw and a replaceable spacer between the lever and the flexure.
In a preferred embodiment, the actuator is a pneumatic bellows, with or without an internal or external spring. A compressible gas supply module is fluidly connected to the bellows. A control module in communication with the compressible gas supply module is used to operate the bellows. An optional sensor module is used to monitor a parameter relating to lens position and/or alignment and to provide data to the control module for automated positioning of the first support relative to the second support.
In a preferred embodiment, two actuators are connected to the lever. Both actuators can be used to make fine adjustments to the position of the lever. Preferably, one actuator (vernier actuator) is used to make finer adjustments to the position of the lever than the second actuator (primary positioning actuator). The vernier actuator can be connected to the lever, for example, either on the same side or the opposite side of a pivot with respect to the primary positioning actuator. In an embodiment, one actuator (i.e., the vernier actuator) is used to make position adjustments of the lever on an order of one-twentieth of the position adjustments typically made by the other actuator (i.e., the primary positioning actuator). Multiple primary positioning actuators, used to control a single axis of motion, can be connected to a common control source (e.g., a pressure source) thus reducing tilt or rotation errors due to control system variations.
It is a feature of the invention that it can be used to position one or more lenses of an optical system to correct or compensate for a variety of changes, including changes that occur in a photolithography optical reduction system that limit the size of semiconductor features that can be accurately reproduced.